1. Field of the Invention
The present invention relates to a process for the continuous production of isophthalodinitrile. More in particular the present invention relates to a process for the continuous production of isophthalodinitrile by amidation and simultaneous dehydration of the dimethyl ester of isophthalic acid in vapor phase on a fixed bed of a dehydration catalyst.
2. Prior Art
The possibility of producing phthalodinitriles starting from the esters of the corresponding acids is long known; for example the UK Pat. No. 737.409 claims the synthesis of phthalodinitrile from a dialkyl phthalate by reaction with ammonia in vapor phase on a catalytic dehydration bed at a temperature comprised between 300.degree. and 600.degree. C.
While in the case of the preparation of terephthalodinitrile, it is possible to obtain a very good yield (approximately 97.5% of theoretical), in the case of isophthalodinitrile, due to the lesser stability of the product, a considerably lower yield is obtained which is fully unsatisfactory for industrial production. More in particular said patent exemplifies the preparation of isophthalodinitrile from diethyl isophthalate by reaction with ammonia in vapor phase on a silica gel bed at a temperature of 450.degree. C.; the high temperature used, however, merely allows a fully unsatisfactory yield (61%).
It is also known (DTAS 1.279.020) to synthesize terephthalodinitrile starting from the dimethyl ester of terephthalic acid by reaction with ammonia in vapor phase on a dehydrating alumina bed at markedly more moderate temperatures, i.e. at 350.degree.-360.degree.. The nitrile which is obtained after being purified, by washing with methyl alcohol, from the colored impurities and by the terephthaldiamide polluting the reaction crude, has melting points (220.degree.-222.degree. C.) and yields (95-97%) very close to the theoretical values. When however one tries to apply said conditions indicated in DTAS 1.279.020 to the synthesis of isophthalodinitrile, the conversion is not as satisfactory (75-80%). Moreover the catalyst is contaminated by degradation products so as to rapidly reduce its activity.